Recreational boats and other marine craft are typically powered by engines that burn either gasoline or diesel fuel. Such boats have at least one fuel tank to hold the liquid fuel until it is delivered to the engine.
Conventional fuel tanks have a fill tube through which the tank may be filled with fuel from the nozzle of a conventional gas pump. A removable cap is usually installed at the end of the fill tube. The cap is removed when the fuel delivery nozzle is inserted into the fill tube to add fuel to the tank.
As liquid fuel is added to the tank, it displaces the air therein. To enable the air in the tank to escape, a vent line is typically used to connect the head space above the level of the liquid fuel in the tank, to the atmosphere. If the vent line were not provided, the air in the headspace of the tank would escape upward through the fill tube as fuel is added. This may cause fuel to splash out onto the operator. The vent line from the fuel tank is typically connected to an opening through the hull of the boat located above the water line.
The vent line also serves to maintain the head space of the tank at atmospheric pressure even when the cap is installed on the fill tube. This enables the fuel in the tank to expand with increasing temperature and prevents the build up of pressure in the tank that could otherwise cause the tank to burst. The vent line also enables fuel to be drawn from the tank to the engine by suction.
A problem with conventional marine fuel systems has been the discharge of fuel from the fuel tank vent line into the water. This problem occurs in a number of circumstances. First, when the tank is being filled with fuel, the agitation of the fuel causes the formation of foam. As the tank reaches a near full condition, the foam is pushed out the vent line into the water. Even if the amount of foam is small, some liquid fuel will usually flow out of the vent line and into the water as the tank is topped off. Some fuel systems are actually designed so that the operator knows that the tank is full when fuel is visually observed flowing out of the vent line. Also, rocking of the boat by wave action as it is being filled with fuel increases the chances that fuel will be pushed out the vent line during the fueling process.
Fuel spillage out of the vent line also occurs when the tank is full and the fuel expands with increased temperature. The expanding fuel typically passes out of the vent line and into the water. Similarly, when a boat with full fuel tanks gets underway, the wave action often causes fuel to flow out of the vent line.
The prevention of fuel spillage from a vent line has been achieved using a number of devices previously patented by the assignee of the present invention. U.S. Pat. Nos. 4,963,169, 5,019,141, and 5,035,729 disclose devices that may be installed in the vent line of a fuel tank to prevent the discharge of liquid fuel therethrough while maintaining the tank vented to atmosphere. Another attempt to solve this problem is shown in U.S. Pat. No. 4,854,469.
In some situations, when fuel is being added to a tank at a very high flow rate, the amount of air being passed through the vent line may cause problems with devices used to prevent discharge of fuel. When using devices like those shown in U.S. Pat. No. 5,019,141, Applicant has found that the buoyant check ball used to prevent the flow of fuel through the device, may be displaced by high air and vapor flow to a position which restricts the flow of air and vapor through the device. Such restriction may occur even when no liquid is present. When this happens, the ability of the device to maintain the tank vented to atmosphere is adversely affected. This may result in premature shut off of the fuel fill nozzle or require filling the fuel tank at a somewhat slower rate. This is not desirable as recreational boaters often want to fill their fuel tanks as rapidly as possible.
Thus, there exists a need for a device that prevents the discharge of liquid fuel through a fuel tank vent line but which enables the passage of air and vapor therethrough at high flow rates.